The broad objective of the proposed research is to elucidate the effects of clozapine treatment on subpopulations of midbrain dopaminergic neurons. Specifically, the molecular and neurochemical changes in NMDA-mediated glutamate transmission induced by acute (1d) versus chronic (21d) treatment of clozapine will be evaluated through two aims. In the first aim, the prefrontal cortex and nucleus accumbens of rats will be injected with retrograde tracer prior to acute or chronic clozapine (or vehicle) treatment. Following drug administration, mRNA from retrogradely-labeled mesolimbic or mesocortical dopaminergic neurons will be amplified and hybridized to a custom cDNA microarray for determination of global changes in gene expression. In the second aim, microdialysis will be used to evaluate changes in extracellular dopamine in the prefrontal cortex and nucleus accumbens, as well as glutamate in the midbrain, after acute and chronic clozapine. In addition, the functional response of midbrain dopaminergic neurons to NMDA and AMPA antagonists will be analyzed based on changes in dopamine release in response to these compounds. These studies will further our understanding of atypical neuroleptic action, and in doing so, may help elucidate the underlying neuropathology of schizophrenia, in addition to identifying ways of improving current pharmacotherapies.